The invention relates to a method of aligning the rotational position of rotatable objects or of positioning translatable objects into a set orientation or position, in particular for aligning optically readable disc-shaped information carriers. The objects are preferably optically scanned line by line in a direction transverse to their direction of movement. After detection of a reference picture line with an optically characteristic picture content, the objects are aligned or positioned.
In engineering it is often required to position or to align objects either for reasons of appearance or for technical reasons. Particularly in automated production or processing operations it is often necessary for an object to have a specific position or orientation. Thus, suitable objects can be positioned by scanning their exterior shape and subsequently bringing them into a specific position. However, this is not always possible. For example, rotationally symmetrical objects cannot be aligned in a specific rotational position by mechanical scanning only. Optical criteria should also be applied.
Known methods of aligning the rotational positions of rotatable objects or for positioning translatable objects based on optical principles, necessitate an optical marking on the object. The objects are then aligned or positioned relative to this optical marking. It is then important that the marking be optically distinct from other parts of the surface of the object. In other words, the marking should bear a minimal resemblance to other parts of the surface of the object. However, this means that the marking used for aligning or positioning the object is distinctly visible. This may not always be desirable; particularly in the case of objects whose physical appearance is important, for example, if for commercial reasons a marking of the type described above must be as inconspicuous as possible. In general, it may even be desirable for such objects to have no specific optical marking provided for the purpose of positioning.